Selectively operable stop mechanisms for blocking and releasing articles conveyed on gravity or powered roller conveyors are common in the art and a wide variety of mechanisms have been employed for actuating such stops to blocking and retracted positions. The various criteria for completely dependable action under all possible conditions render the provision of a simple mechanism meeting all requirements a more difficult problem than apparent from initial consideration. In view of the impact and cumulative loads that may build up against the stop, there is a need for a blocking action of the stop which can withstand considerable force without yielding; since it is frequently necessary for the stop to be retracted under a highly loaded condition it is necessary to accommodate or eliminate friction in the linkage components which provide the holding resistance when it is desired to release the stop; at the same time it is desirable that the stop may be released without drag on the article which might otherwise cause wear or damage; it is desirable that any mechanism for returning the stop from retracted to blocking position be rendered automatically inoperative during any overpassing of an article while being capable of immediately moving to a stop position as soon as the trailing edge of the article has passed so as to be capable of intercepting the next article in case it is following in close proximity to that passing over the stop; it is desirable to accomplish these objectives with a simple solenoid actuation preferably de-energized when the stop is in operative position; it is desirable to stop and engage the leading edge of an article in a manner which will avoid overriding from the impact of either a single load or other loads behind it. In the end it is, of course, desirable that all of these objectives be met with a construction which is as simple and inexpensive as possible.